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'[EE]: Infrared Detector vs Pet'
2001\02\27@110809 by Simon Ethier

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Hi, I'm wondering.. I heard in a publicity of an alarm company that they have an infrared detecter which can make the difference between pet and human (how, I don't know ... ok it don't really "make" the difference, but the IR won't react to a cat for exemple, but will react to a human) I found this very cool, especially if you have pet at your house...
I'd like to build something like that ... Do any of you guys know what is the trick ?  Is it less sensitive ? Does it require a minimum of movement ...  
Thanks
---
Simon Ethier
spam_OUTsethierTakeThisOuTspamjustine.umontreal.ca
ICQ 66019153

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2001\02\27@114202 by Ray Russell

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In a message dated 2/27/01 11:10:08 AM Eastern Standard Time,
.....Seth889KILLspamspam@spam@STARTREKMAIL.COM writes:


{Quote hidden}

Simon,
I use these detectors in my shop. They produce a multi path beam. Multiple
beams must be broken in both directions to set them off. We had a problem
with rodents getting into the shop. (We are in the country so field mice and
rats are common)
They kept setting off the old detectors. Even the mouse traps would set the
darn things off. The new ones are very sensative to humans but cats and mice
seem not to bother it at all!

Ray Russell
General Contractor
Norfolk & Western Railroad

Pocahontas Division
Circa 1958
Visit The Pocahontas Website at:
<A HREF="http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm">Click here: Pocahontas Home</A>
OR
http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm

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2001\02\27@115218 by Simon Ethier

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Any idea on how to build this ?

thanks
---
Simon Ethier
sethierspamKILLspamjustine.umontreal.ca
ICQ 66019153

{Original Message removed}

2001\02\27@120212 by Justin Fielding

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I assume that you are talking about IRbeams (which must be broken to trigger
alarm) rather than a PIR detector (using a pyrometer).


{Original Message removed}

2001\02\27@122132 by Simon Ethier

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I don't really know ... All I'd like to do is build a cheap but effective
"IR" detector that do not triggers with pets like cats ...

Thanks

{Original Message removed}

2001\02\27@122808 by Justin Fielding

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Lookup pyrometers, they may be a good way to do this as you could adjust the
sensitivity.  They actually work by detecting movement of body heat ( I
think).  With an IR beam it is all or nothing,


{Original Message removed}

2001\02\27@123004 by Ray Russell

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In a message dated 2/27/01 11:54:17 AM Eastern Standard Time,
.....Seth889KILLspamspam.....STARTREKMAIL.COM writes:


> Any idea on how to build this ?
>
> thanks
> ---
> Simon Ethier
>

Simon,
Sorry the alarm co. installed them so they are off the shelf items. Sealed
unit and only alarm co numbers on it so I cannot point you in the right
direction.

Ray Russell
General Contractor
Norfolk & Western Railroad

Pocahontas Division
Circa 1958
Visit The Pocahontas Website at:
<A HREF="http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm">Click here: Pocahontas Home</A>
OR
http://milliron.home.sprynet.com/Pocahontas/Pocahontas1.htm

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2001\02\27@125043 by O'Reilly John E NORC

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You might want to check surplus houses for already built ones.  I know All
Electronics (http://www.allelectronics.com/) has a wireless PIR ($5.50) and
associated receiver ($5.50).

{Original Message removed}

2001\02\27@125249 by Terry

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Do a search for "passive infra red detector". You should be able to find a
circuit using a dual element pyroelectric detector. Off the shelf detectors
are going for something like SG$10.00 - $20.00 and come with various
fresnel lens. Normal, long range, curtain, etc.

Depending on how you mount the detector, type of lens and sensitivity
setting, it could trigger when the sun shines into the room, a radiator
turning on or a rodent paying a visit. Most detectors are pretty reliable
and not prone to false triggering if you set it up correctly. Look at the
leaflet that comes with it, it'll show the top and side views of the
"beams" (they're actually detection zones).


At 12:21 PM 2/27/01 -0500, you wrote:
>I don't really know ... All I'd like to do is build a cheap but effective
>"IR" detector that do not triggers with pets like cats ...
>
>Thanks
>
>{Original Message removed}

2001\02\27@133305 by James Paul

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Justin,

Typically I believe the way these things discriminate between man
and beast is that they aim the devices so that the bottom of the
cone of coverage is about 2-3 feet off the floor.   That way, most
house pets won't set off the alarm because it is not within the
transmitted beam.   However, humans, being substantially taller
than most house pets, is within the beam, and does set off the
alarm.

                                         Regards,

                                           Jim








On Tue, 27 February 2001, Justin Fielding wrote:

>
> Lookup pyrometers, they may be a good way to do this as you could adjust the
> sensitivity.  They actually work by detecting movement of body heat ( I
> think).  With an IR beam it is all or nothing,
>
>
> {Original Message removed}

2001\02\27@141344 by Simon Ethier

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Humm, I don't think so ... What for the cat that climb on the sofa, or on a
bookshelf ?

hehe

----- Original Message -----
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To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Tuesday, February 27, 2001 1:33 PM
Subject: Re: [EE]: Infrared Detector vs Pet


{Quote hidden}

the
{Quote hidden}

effective
{Quote hidden}

they
> > > > have an infrared detecter which can make the difference between pet
and
> > > > human (how, I don't know ... ok it don't really "make" the
difference,
> > but
> > > > the IR won't react to a cat for exemple, but will react to a human)
I
> > > found
> > > > this very cool, especially if you have pet at your house...
> > > >
> > > > I'd like to build something like that ... Do any of you guys know
what
{Quote hidden}

subtopics
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2001\02\27@142420 by Pedro Drummond

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Man from beast ? By their weight difference ! The more mass, the more
infrared density emission.



{Original Message removed}

2001\02\27@145105 by Justin Fielding

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Im not sure that is how they work, I read about them in the mobile robotics
book.  the more heat an object emits the larger the output pulse so you
could set the sensitivity by ignoring all pulses below a certain level.  You
can also tell which direction an object is travelling in by analysing the
output.  I cant remember much about them, just a few bits from that book so
I may be wrong.


{Original Message removed}

2001\02\27@152052 by Sean Breheny

face picon face
Doesn't clothing effect the emissivity of a person? I would think that a
moderately sized pet (medium size dog) with black fur might emit more IR
than a person clothed in white, so differentiating between people and
animals based on amount of heat might not work reliably. Then again,
perhaps a person has so much more surface area that it more than makes up
for the lower emissivity, I don't know.

What about using a metal-covered plastic parabolic reflector with the PIR
at its focus? You could place a small disk in front of the PIR to make
the instrument's FOV have a dead zone in the center. This would require
an IR emitting object to be larger than a certain size in order to be
detected. There may be a way to do this with a specially molded or
modified plastic lens (like they have on most PIR modules).

One problem is that an object very close to the sensor would appear
larger than one farther away, which would mean that a sensor like this
could only cover a limited area (i.e., a person who is too far away would
appear as small as a dog and not be detected).

Sean


On Tue, 27 Feb 2001, Justin Fielding wrote:

> Im not sure that is how they work, I read about them in the mobile robotics
> book.  the more heat an object emits the larger the output pulse so you
> could set the sensitivity by ignoring all pulses below a certain level.  You
> can also tell which direction an object is travelling in by analysing the
> output.  I cant remember much about them, just a few bits from that book so
> I may be wrong.
>
>
> {Original Message removed}

2001\02\27@152907 by t F. Touchton

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part 1 8517 bytes content-type:text/plain; charset=us-asciiMy limited experience with furry critters seemed to indicate the opposite.  Was
trying to detect squirrels with a PIR system for remote camera activation.  The
PIR had a heck of a time seeing them.  I thought that the fur may be at the
ambient temp, and not at the squirrel body temp.  Seemed as if there was no
discernible moving heat signature for the PIR to see.


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Doesn't clothing effect the emissivity of a person? I would think that a
moderately sized pet (medium size dog) with black fur might emit more IR
than a person clothed in white, so differentiating between people and
animals based on amount of heat might not work reliably. Then again,
perhaps a person has so much more surface area that it more than makes up
for the lower emissivity, I don't know.

What about using a metal-covered plastic parabolic reflector with the PIR
at its focus? You could place a small disk in front of the PIR to make
the instrument's FOV have a dead zone in the center. This would require
an IR emitting object to be larger than a certain size in order to be
detected. There may be a way to do this with a specially molded or
modified plastic lens (like they have on most PIR modules).

One problem is that an object very close to the sensor would appear
larger than one farther away, which would mean that a sensor like this
could only cover a limited area (i.e., a person who is too far away would
appear as small as a dog and not be detected).

Sean


On Tue, 27 Feb 2001, Justin Fielding wrote:

> Im not sure that is how they work, I read about them in the mobile robotics
> book.  the more heat an object emits the larger the output pulse so you
> could set the sensitivity by ignoring all pulses below a certain level.  You
> can also tell which direction an object is travelling in by analysing the
> output.  I cant remember much about them, just a few bits from that book so
> I may be wrong.
>
>
> {Original Message removed}
part 2 7779 bytes content-type:application/octet-stream; (decode)

part 3 144 bytes
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2001\02\27@153946 by Sean H. Breheny

face picon face
Hi Scott,

Perhaps you are right, maybe the outer layer of fur is cool and obscures
the inner layer. Also, I realized that my idea is a little messed up (you
don't want a dead zone), and I don't have time at the moment to figure out
if there is an optically feasible means to reject small objects :-)

Sean

At 03:22 PM 2/27/01 -0500, you wrote:
{Quote hidden}

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>   |       cc:     (bcc: Scott
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> Pet                     |
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> > {Original Message removed}

2001\02\27@154812 by t F. Touchton

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part 1 11627 bytes content-type:text/plain; charset=us-asciiPerhaps one can do some type of a dual zone PIR.  Something that looks across a
specific height to be triggered (such as 2 PIR's... one looking 2' off the
ground and one looking 4' off the ground).  That way an object smaller than 2'
hovering in the air (or on the couch) will (should?) have much less chance of
triggering.

The PIR's I worked with are dual MOSFET style designs.. basically looking for
horizontal motion and mounted in a horizontal orientation.  Wondering if you
could flip this to a vertical plane and somehow use this to ones advantage...
the Fresnel lens would need to accomodate this too.


|--------+----------------------->
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Hi Scott,

Perhaps you are right, maybe the outer layer of fur is cool and obscures
the inner layer. Also, I realized that my idea is a little messed up (you
don't want a dead zone), and I don't have time at the moment to figure out
if there is an optically feasible means to reject small objects :-)

Sean

At 03:22 PM 2/27/01 -0500, you wrote:
{Quote hidden}

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> Pet                     |
>
>
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> > {Original Message removed}
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2001\02\27@161058 by Thomas McGahee

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About 4 years ago one of my students managed to get a sensor
donated (cosmetic defect) that I believe was a very large area
brown colored chip. Chip was about 1/2 inch square mounted in a
round package about 3/4 inch round with a top that was optically
clear. This thing had just two wires. I designed a simple
op-amp circuit that would respond only to changes in output.
I used a current to voltage coverter at the front end to get
maximum sensitivity. This thing was quite amazing. It was
extremely sensitive to the radiation emitted by humans. What
I found interesting was that it had no trouble at all detecting
a human through several layers of clothing, including heavy
winter coats. It did not seem to be "infra-red" detecting in the
sense that we normally use that word. It was sort of
tuned to the specific heat signature of the human body. It
could even detect this heat signature when the detector was
covered with a sheet of aluminum foil. In fact, one of our
major problems was preventing it from picking up signals
that were coming in from the sides (and even the BACK!).

But it ignored squirrels. (Never tried it on a cat).
I don't think it was the fur that prevented detection,
because we had one person acting as our target who
had TWO very thick coats on, gloves, and two hats facing
with their back to the sensor, and they were easily
detected.

Unfortunately I can't seem to find the project report in any
of my filing cabinets at the moment, but I vividly
remember how it could detect humans with great ease.

It could be that the detector being touted by this company
actually responds to the specific human body signature,
just like the sensor in our project.

Fr. Tom McGahee


{Original Message removed}

2001\02\27@162317 by Simon Ethier

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It seems pretty good .. if you ever find the report and could give me more
info, it would be very appreciated ...

thanks
{Original Message removed}

2001\02\27@162745 by Justin Fielding

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Body's capacitance?  something of the sort.


----- Original Message -----
From: "Thomas McGahee" <RemoveMEtom_mcgaheeKILLspamspamSIGMAIS.COM>
To: <PICLISTSTOPspamspamspam_OUTMITVMA.MIT.EDU>
Sent: Tuesday, February 27, 2001 9:16 PM
Subject: Re: [EE]: Infrared Detector vs Pet


{Quote hidden}

(you
> > don't want a dead zone), and I don't have time at the moment to figure
out
{Quote hidden}

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2001\02\27@172632 by Jinx

face picon face
> Body's capacitance?  something of the sort.

PIRs will work up to quite long distances with the right lens
so I doubt if C has much effect. You're looking for an output
from the sensor around 1Hz. It can be quite a balancing act
making a PIR responsive to humans and not responsive to
wafts of cold/warm air

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2001\02\27@174717 by Scott Dattalo

face
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On Wed, 28 Feb 2001, Jinx wrote:

> > Body's capacitance?  something of the sort.
>
> PIRs will work up to quite long distances with the right lens
> so I doubt if C has much effect. You're looking for an output
> from the sensor around 1Hz. It can be quite a balancing act
> making a PIR responsive to humans and not responsive to
> wafts of cold/warm air

Check out this:

http://www.4qd.co.uk/ccts/pdet.html

It's an e-field sensor (capacitance) that's so sensitive that it can detect when
a person enters a room. The circuit was designed in the 70's and as the web
says:

    it appeared to be a male circuit as it tended to react
    more to women than to men. I haven't tested that and
    suspect it would not be true today. In the 70's women
    wore more nylon clothing than did men and antistatic
    fabrics were unknown.


You'd be surprised at how easy it is to measure a delta C. Essentially that's
what we do at Synaptics (my current employer). We make most of the touch pads in
lap tops. In our application, we sense fingers instead of "people". Proximity is
obviously a factor. But as the web page I site above indicates, the technique
scales. (although our technique is nothing like their's).

Scott

PS. btw, we're hiring If anyone's interested.

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2001\02\27@181520 by Jinx

face picon face
> http://www.4qd.co.uk/ccts/pdet.html

You've reminded me of it. I had the main page URL tucked
away somewhere a while ago,even think I passed it on to
one or two people. Might knock one up JFTHOI to see if it
might be more suitable in some instances than PIRs, maybe
around doorways that are subject to strong sunlight and
drafts

The long range I mentioned before is a 100ft claim by the lens
mftr. IIRC though they use IR floodlighting and a curtain Fresnel,
intended for areas like fenced parking or commercial areas at
night to detect perimeter intrusion

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2001\02\27@190933 by Justin Fielding

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Yes, that is the type of thing I was referring to, I was not saying that a
PIR was being effected by C but that the sensor described was not a PIR.

:)

Justin.

{Original Message removed}

2001\02\27@213049 by Jinx

face picon face
> Yes, that is the type of thing I was referring to, I was not saying
> that a PIR was being effected by C but that the sensor described
> was not a PIR

My apologies. Compared to most animals that we encounter
around the home (cats dogs birds rodents) humans would have
a definitely detectable C presence

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2001\02\27@215752 by Olin Lathrop

face picon face
> Doesn't clothing effect the emissivity of a person? I would think that a
> moderately sized pet (medium size dog) with black fur might emit more IR
> than a person clothed in white,

As an aside, black objects are better thermal radiation (black body)
emitters than white objects.  This is a common misconception because black
objects are also better thermal radiation absorbers.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, EraseMEolinspamEraseMEembedinc.com, http://www.embedinc.com

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2001\02\27@221527 by Jinx

face picon face
> > Doesn't clothing effect the emissivity of a person? I would think
> > that a moderately sized pet (medium size dog) with black fur
> > might emit more IR than a person clothed in white,
>
> As an aside, black objects are better thermal radiation (black
> body) emitters than white objects.  This is a common miscon
> ception because black objects are also better thermal radiation
> absorbers.

In the case of fur, colour is not the determining factor - it's how
much heat gets to the surface from the body. Although a black
fur next to a white fur on a sunny day would look hotter because
the sun heat it was absorbing at its surface

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2001\02\27@233525 by Sean H. Breheny

face picon face
Hi Olin,

Yes, that's what I was saying, the black object (at the same temperature)
would probably emit better than the white object. I say probably because I
don't know if all objects which are black at visible wavelengths are also
black bodies at IR.

It's a basic consequence of thermodynamics. If an object were a better
emitter than it is an absorber, it would spontaneously cool below the
ambient temperature. The other way around and it would spontaneously  get
warmer.

Sean

At 06:13 PM 2/27/01 -0500, you wrote:
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2001\02\28@025943 by Vasile Surducan

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There is no difference between a standard IR detector and a "not pet IR
detector " except the front fresnel plastic lens and the sensitivity,
which is in fact the gain of input operational amplifier stage.
This analogic signal is compared into a windows comparator. One pulse or
multiple pulse are resolved with a simple RC integrator.
I was talking about cheap IR detectors ( relay and tamper) and not those
who are connected between on a smart bus.
You may built yourself if this is your passion, buy from EG&G Heimann
a pyroelectric infrared sensor with built in filter at 5..14um vavelenght
( where human body radiation is maximum )
You may choose from a large range of infrared sensors.
You need also a low noise operational amplifier, a comparator, and a lot
of working...

Vasile



On Tue, 27 Feb 2001, Simon Ethier wrote:

> Any idea on how to build this ?
>
> thanks
> ---
> Simon Ethier
> spamBeGonesethierspamKILLspamjustine.umontreal.ca
> ICQ 66019153
>
> {Original Message removed}

2001\02\28@035016 by Andy Stubbins

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picon face
For those who plan to build a PIR (whether man or beast) or just want to
know exactly how they work, here is an excellent link
http://www.glolab.com/pirparts/infrared.html
It seems this nice chap has done all the hard work already! including
circuit diagrams.



{Original Message removed}

2001\02\28@090534 by Olin Lathrop

face picon face
> > As an aside, black objects are better thermal radiation (black
> > body) emitters than white objects.  This is a common miscon
> > ception because black objects are also better thermal radiation
> > absorbers.
>
> In the case of fur, colour is not the determining factor - it's how
> much heat gets to the surface from the body. Although a black
> fur next to a white fur on a sunny day would look hotter because
> the sun heat it was absorbing at its surface

I agree.  The only reason I brought this up is because the original poster
made a special point of the fur color.  As an additional aside, some animals
seem to have evolved fur that have special properties with respect to IR and
visible radiation.  Polar bears are being studied for this.  You may need a
different IR sensor if you live in an igloo ;-)


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Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, .....olinspam_OUTspamembedinc.com, http://www.embedinc.com

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2001\02\28@091344 by t F. Touchton

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face
part 1 2641 bytes content-type:text/plain; charset=us-asciiJust some more observations on color:   I have several PIR sensors controlling
lights in my basement.  I have 2 winter coats that I store in the basement: one
black and one grey.  When I wear the grey coat, the PIR sensors all work fine.
When I wear the black coat, I have to jump up and down and wave my arms to get
the PIR sensors to activate.  The black coat is not nearly as heavy and warm as
the grey coat....  I guess its time to get a far-IR viewer to see whats going
on!


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|        |                           |
|        |          02/28/01 08:09 AM|
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 |       cc:     (bcc: Scott Touchton/US/UNIPHASE)                            |
 |       Subject:     Re: [EE]:  Infrared Detector vs Pet                     |
 >----------------------------------------------------------------------------|





> > As an aside, black objects are better thermal radiation (black
> > body) emitters than white objects.  This is a common miscon
> > ception because black objects are also better thermal radiation
> > absorbers.
>
> In the case of fur, colour is not the determining factor - it's how
> much heat gets to the surface from the body. Although a black
> fur next to a white fur on a sunny day would look hotter because
> the sun heat it was absorbing at its surface

I agree.  The only reason I brought this up is because the original poster
made a special point of the fur color.  As an additional aside, some animals
seem to have evolved fur that have special properties with respect to IR and
visible radiation.  Polar bears are being studied for this.  You may need a
different IR sensor if you live in an igloo ;-)


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, TakeThisOuTolinKILLspamspamspamembedinc.com, http://www.embedinc.com

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part 2 3332 bytes content-type:application/octet-stream; (decode)

part 3 131 bytes
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2001\02\28@105731 by Simon Ethier

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face
I don't have access to  EG&G Heimann since I suppose they are in the US ...
I'm in Canada .. Do they have a website ?

thanks

{Original Message removed}

2001\02\28@175814 by Jinx

face picon face
> I agree.  The only reason I brought this up is because the original
> poster made a special point of the fur color.  As an additional aside,
> some animals seem to have evolved fur that have special properties
> with respect to IR and visible radiation.  Polar bears are being
> studied for this

And as another aside, the fact that animals such as Arctic foxes
and hares change coat colour to white in winter rather than keep
a dark colour to absorb heat shows that any absortion just happens
at the surface of the fur. Obviously the insulation of any colour fur
is sufficient and the better survival tactic is camouflage. Not
thoroughly [OT] yet, if you consider how nature can produce such
an excellent insulator as duck down, which I believe has yet to be
bettered by the boffins

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2001\02\28@194516 by Reginald Neale

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face
> > Doesn't clothing effect the emissivity of a person? I would think that a
> > moderately sized pet (medium size dog) with black fur might emit more IR
> > than a person clothed in white,
>
>As an aside, black objects are better thermal radiation (black body)
>emitters than white objects.  This is a common misconception because black
>objects are also better thermal radiation absorbers.


  As a further aside, it should be kept in mind that the visible
  appearance of an object is not a reliable guide to its
  emissivity in the far IR.

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'[EE]: Infrared Detector vs Pet'
2001\03\01@063632 by Vasile Surducan
flavicon
face
Well if you live in Canada don't bother, you have there some of the best
pir detectors from the world, I'm speaking about Bravo series from DSC.
I know Bravo2 and Bravo3, the last one is cheap enough ( here is about
15...22 USD, there must be under 12 USD ) If I remember well Bravo3 has
trim inside for sensitivity reglage and an extra piezoelectric sensor for
noise detection. Maximum range for this volume sensors is about 18m but if
you need to "loose" smal beast you must decrease this range at max 5m and
sometime under this limit.
Also the piroelectric sensors are made with different filter, the common
one is 5...14um wavelenght but you may ask a special one from 8 to 14um
wich feet better whith human radiation.
If you want to calculate your own filter here is the formula

labda(um)=T (K) * 2880

where labda is wavelenght measured in micrometers
T           is human or beast temperature measured in kelvin degrees
and const byte = 2880

You have nothing to do else that to take medium temperature of your pet
and design your own filter. However these filters are made by thin silicon
and can't be exchanged on the same sensor. If you break the filter you can
drop to garbage the whole pir detector.
I don't keep secret that asking for a custom filter is possible to cost
you a fortune, much more than some clever tricks with a standard and cheap
PIR detector one.

Vasile




On Wed, 28 Feb 2001, Simon Ethier wrote:

> I don't have access to  EG&G Heimann since I suppose they are in the US ...
> I'm in Canada .. Do they have a website ?
>
> thanks
>
> {Original Message removed}

2001\03\01@072049 by Mark Moldavsky

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face
Hi,Justin.

One of the possible solutions you can find in http://www.visonic.com.

Best regards.
Mark.



Justin Fielding wrote:

> I assume that you are talking about IRbeams (which must be broken to trigger
> alarm) rather than a PIR detector (using a pyrometer).
>
> {Original Message removed}

2001\03\01@123600 by rottosen

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face
I have a friend that works with IR laser diodes. He says that it is very
hard to guess the reflectivity of IR by looking at something. Things
that LOOK black do not always absorb IR.

Also, he says that one of the best black surfaces (for IR) he has found
is black conductive foam.


-- Rich

"Sean H. Breheny" wrote:
{Quote hidden}

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2001\03\01@124436 by Alan B. Pearce

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>I have a friend that works with IR laser diodes. He says that it is very
>hard to guess the reflectivity of IR by looking at something. Things
>that LOOK black do not always absorb IR.

>Also, he says that one of the best black surfaces (for IR) he has found
>is black conductive foam.

A colleague I used to work with was into motorbikes, especially painted black.
He had some theory that black paint was actually transparent at either IR or UV,
to get the black colour by diffraction. He reckoned you tell which end of the
spectrum it was transparent at by looking at a reflective sheen from sunlight.
If it had a blue hue to it then it was transparent at UV, if a red hue then
transparent at IR.

How true this might be I do not know, but at the time it seemed to make sense.

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2001\03\01@165846 by rottosen

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"Alan B. Pearce" wrote:
>
> >I have a friend that works with IR laser diodes. He says that it is very
> >hard to guess the reflectivity of IR by looking at something. Things
> >that LOOK black do not always absorb IR.
>
> >Also, he says that one of the best black surfaces (for IR) he has found
> >is black conductive foam.
>
> A colleague I used to work with was into motorbikes, especially painted black.
> He had some theory that black paint was actually transparent at either IR or UV,
> to get the black colour by diffraction. He reckoned you tell which end of the
> spectrum it was transparent at by looking at a reflective sheen from sunlight.
> If it had a blue hue to it then it was transparent at UV, if a red hue then
> transparent at IR.
>
> How true this might be I do not know, but at the time it seemed to make sense.
>

I don't know about that but here is another bit of insight.

I worked on a project that needed molded parts for prototyping. A master
part was machined and polished out of aluminum. Then a silicon rubber
mold was made using the master. The mold was then used to make a black
epoxy part. This part was a shiny black color. When it was decided that
the molded part was too shiny, the master was painted flat black.
Another mold was made and a new part was cast. The new part was now FLAT
BLACK. I seems that the characteristic of black is not only the color
but the texture as well. Also note that the silicon rubber mold was able
to transfer the "flat" texture to the molded part. That implies to me
that a huge amount of detail is posible using silicon rubber molds.

-- Rich



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2001\03\01@170712 by Dan Goddard

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At 02:56 PM 3/1/01 -0700, you wrote:
{Quote hidden}

Is that why the stealth bomber is flat black? hehe :)

Dan


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2001\03\02@080108 by Alan B. Pearce

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>Is that why the stealth bomber is flat black? hehe :)

I suspect this may have more to do with the RF absorbing characteristics of the
paint, but I take your joke. :)

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